what is the average thickness of the floor/ceiling between levels in a multi-leveled house?

Question

I am drawing up house plans but need to know how thick to make the flooring between the 1st and 2nd floors

Answer 1

Use the span tables out of your local Building Code to determine the size of the joists you will require in relation to the span between supports.
The National Building Code permits 2x6 @ 16" c/c to span 9' 5". If your span is greater you will most likely need 2x8 or 2x10. For large spans, (greater than 14ft), pre-engineered floor joist systems are available. Check with your local building supply store.
The total height will be the nominal size of your floor joists, ie; 6" is actually 5 1/2", and 8" is actually 7 1/4", plus your subfloor which is usually 3/4" plywood or OSB, plus your finished ceiling which is usually 1/2" or 5/8" drywall.

Answer 2

It depends on floor joists and span. The longer the span, the deeper the joist. Typically, home builders and designers limit the span to 16'. Therefore, the depth is usually a 2x10. A 2x10 is actually 9-1/4" deep. Or a engineered TGI floor joist is typically 9-1/2" deep. Of course, you can span farther but then you need deeper joists. So the limit of 16' is a balance between economy and open space on the first floor.

So I draw a section using 2x10, 3/4" subfloor and 5/8" ceiling drywall. The floor system is 10" plus the drywall.

Another tip: You need to be able to trace the roof loads down to the foundation. As a designer, the problem I see in other people's designs is the lack of structural understanding of following the loads. The roof load needs to come down on a second floor bearing wall or beam, which needs to be over a first floor bearing wall or beam, which needs to be over a foundation wall or beam. You need to design the structural elements from the roof down to the foundation, not from the foundation up, which is the common mistake. I know this is a little off topic, but I've seen this mistake so many times, I think I need to mention it. If in doubt, talk to some framers, engineers, or professional designers. Another source would be the local building department. Just found this site, also:

http://www.eng-tips.com/threadcategory.cfm?lev2=21

The reason I mention this is you seem to be a novice. No offense, because everyone has to start somewhere. I encourage your efforts, but designing a two story house requires special consideration of structures. So I strongly recommend that you have some experts look at you design. It will be a lot easier to fix a mistake on paper than after the inspector has shot down the framing, or worse, you discover the floor in this new house is deflecting an inch, drywall is cracking, tile is cracking and doors frames are now completly out of square.

Good luck

Answer 3

The average 2nd floor use is a 2x12 depending on the span of the room plus the 3/4 in. decking. is the ceiling below over a garage? if so the drywall should be 2 layers thick for firewall codes. the 2x12s are now from 11 1/4 to 11 1/2 wide plus the 3/4 decking plus two thicknesses of 5/8 drywall if needed. You do the math. Why are you asking this anyway?

Answer 4

Using 2x6 floor joists, the average width of a 2x6 is 5 and 1/2 inches. The plywood floor is roughly 3/4 inches. The ceiling underneath the 2nd floor is covered in 1/2 inch drywall. The floor covering on the 2nd floor is either carpet, tile, or wood flooring. so:
5.5 + .75 + .5 + .5(floor covering) = 7.25 "

Answer 5

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here state side modern buildings like homes are around 8 inches that is a 2x6 joice and floor covering on top and ceiling covering on the bottom commercial buildings are around 10 inches - thats a 2x8 joice plus older homes more than 75 years are around 12 inches - thats a 2x12 plus dimensional wood (when they didn't cheat the measurements a 2x4 was really 2 and 4 inches)

Answer 6

12 inches is the normal "default" thickness used by the design trade ( green 2X12 joists are now barely 11 1/4'' -- when dry 11" plus 1/2 sheetrock ceiling and a 3/4" deck -- thats 12 1/4" to 121/2" ) Can you scale and draw the difference between 12" and 12 1/2" ??? the real question is do you know enough to be even asking the question --let alone design a structure?

Answer 7

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Answer 8

moreover the 2x6 will span 12' with 16" on center, however, if the span is greater in width or on-centers, you need calc's or go to 2x10-2x12 predicated on the span and the dimensions of the room.

Answer 9

The joist dimension depends on the span. (see span tables) , and 5/8 t&g is standard sheathing.

Answer 10

8 to 12 inches depending on your area